Hi,
I don´t really know what advice to give you - besides the obvious, like turning up the volume, setting up the speficic audio levels in the PREFERENCES menu correctly, making sure your hardware works correctly, Windows and X-Plane and all drivers being up to date, etc.
We have heard infrequent reports of some folks with specific audio hardware running out of sound channels, so they can not hear some sounds like the radar altimeter counting down, but we have never had a report like yours...
Cheers, Jan